Page:Life Movements in Plants.djvu/67

Rh It is interesting in this connection to refer tn the response of the leaf of Water Mimosa (Neptunia oleracea). Here the reaction is very sluggish in comparison with that of Mimosa pudica. A tabular statement of contractile response of various radial, anisotropic and pulvinated organs will show a continuity in the contractile reaction: the difference exhibited is a question of degree and not of kind.

As regards the excitatory fall of the leaf of Mimosa pudica, Pfeffer and Haberlandt are of opinion that this is due to the sudden diminution of turgor in the excited lower half of the pulvinus. The weight of the leaf, no longer supported by the distended lower cells, causes it to fall. This is accentuated by the expansion of the upper half of the pulvinus which is normally in a state of compression. According to this view the excitatory fall of the leaf is a passive, rather than an active, movement. I have, however, found that in determining the rapidity of